In order to filter a fluid with hollow fiber membranes, the membranes are fixed to a header, alternatively called a potting head or a tube sheet, such that their outer surfaces are sealed to a first face of the header, but their lumens are open to a second face of the header. In an immersed membrane module the header, with the membranes, is then attached to a permeate pan to create a permeate collection space between the second face of the header and the pan. The permeate collection space is connected to a source of suction to create a trans-membrane pressure across the walls of the membranes and to carry the liquid from the ends of the membranes through the permeate collection space.
In U.S. application Ser. No. 10/167,699, the ends of membranes are potted in a liquid wax to create a fugitive lamina. The wax is allowed to solidify around the ends of the membranes. A thermosetting or thermoplastic synthetic resinous material is then poured over the wax to create a fixing lamina. The wax prevents the ends of the membranes from being plugged with the resinous material. The resinous material is allowed to harden around the membranes into a header. The wax is then removed by, for example, heating or dissolving with a solvent, leaving the ends of the membranes open to a space formerly occupied by the wax.
In U.S. Pat. No. 6,592,759, ends of membranes are potted in a dense gel. A liquid, less dense than the gel, is poured over the gel and around the membranes. The gel prevents the ends of the membranes from being plugged with the liquid. The liquid is allowed to harden into a header. Once the liquid has hardened, the gel is removed by vibrating to a fluid state, flushing with a solvent, or heating.
In U.S. Pat. No. 7,393,486, a bundle of hollow fiber membranes are potted by injection molding a hot thermoplastic into a cavity containing the membranes. The cavity is formed between a mold and two spaced-apart layers of adhesive pre-applied to the bundle of membranes. The hot thermoplastic is allowed to harden into a header.
In U.S. application Ser. No. 12/381,097, ends of membranes are inserted into a spacer and held with open ends protruding upwards from the spacer. The spacer can be a plate with openings to accommodate the membranes or the spacer can be flexible plastic strips. In the case of flexible plastic strips, the strips can be wound up in spiral shape, or segments of plastic strip can be combined to form a multi-layer package. Once the membranes are inserted in the spacer, a liquid is then poured around the membranes and over the top of the spacer. The spacer is non-permeable to the liquid thus preventing the liquid from flowing down the membranes. The liquid is allowed to harden into a header.